(a) Technical Field
The present invention relates to a system and a method for controlling a low voltage DC/DC converter (LDC) of a hybrid vehicle. More particularly, the present invention relates to a system and a method for controlling an LDC of a hybrid vehicle, in which a fuel efficiency mode for artificially turning off pulse width modulation (PWM) control of the LDC is added, thereby improving fuel efficiency.
(b) Background Art
A low voltage direct current/direct current (DC/DC) converter (LDC) of a hybrid vehicle mounted within a hybrid vehicle functions to charge an auxiliary battery by converting high-voltage DC voltage output from a high-voltage battery into a low-voltage DC voltage and to supply electricity suitable for a voltage used in each electric field load by monitoring the amount of voltage used in electric field loads of the vehicle. For reference, the LDC refers to a device configured to switch a DC voltage to an alternating current (AC) voltage, increase or decrease the AC voltage using a coil, a transformer, a capacitor, or the like, and rectify the AC voltage into a DC voltage.
A method for controlling the output voltage of a conventional LDC will be described in regards to FIG. 1 which illustrates a power supply flow of a conventional LDC according to the related art. The voltage control of the LDC 20 is performed in a form in which an LDC controller outputs a voltage instruction.
First, the LDC controller determines a control priority order obtained based on a state of charge (SOC) of an auxiliary battery 30, a use of an electric field load 40, a current driving mode, etc. Then, when the voltage control of the LDC 20 is possible, the LDC controller outputs an output voltage instruction to the LDC 20. Accordingly, the auxiliary battery 30 is charged by an output voltage of the LDC 20, or power is supplied to the electric field load 40 by the output voltage of the LDC 20 (see power supply indicated by arrows of FIG. 1).
In particular, the LDC controller compares an auxiliary battery voltage Vbatt with an output voltage instruction Vref. When the output voltage instruction Vref is greater than the auxiliary battery voltage Vbatt, the LDC controller turns on switching control of a switching element (transistor), i.e., pulse width modulation (PWM) control. Further, when the output voltage instruction Vref is less than the auxiliary battery voltage Vbatt, the LDC controller turns off the PWM control.
In other words, as shown in FIG. 2 of the related art, the conventional LDC 20 performs the PWM control when the output voltage instruction Vref is greater than the auxiliary battery voltage Vbatt, and thus, power of a main battery (high-voltage battery) 10 is supplied to the auxiliary battery 30 and/or the electric field load 40. Accordingly, the LDC is mounted within an eco-friendly vehicle such as an electric vehicle, a hybrid vehicle, or a fuel cell vehicle, to supply power to the electric field load to protect discharge of the auxiliary battery through PWM on control and also to charge the auxiliary battery when the voltage of the auxiliary battery is decreased to a predetermined level or less.
However, in the conventional LDC, the time required to turn on PWM control is substantial to thus supply power to the electric field load and/or the auxiliary battery. Therefore, the consumption of power of the high-voltage battery, supplied to the electric field load and/or the auxiliary battery increases, which results in deterioration of fuel efficiency. When the auxiliary battery is separated to be replaced when the PWM control is turned off or when the auxiliary battery is separated due to external impact or the like, power is not supplied to the electric field load, and therefore, the driving of the vehicle is impossible.